Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch sensor panels, joysticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device that can be positioned behind the panel so that the touch-sensitive surface can substantially cover the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
Touch sensor panels can be formed from a matrix of drive lines and sense lines, with sensors (pixels) located where the drive and sense lines cross over each other while being separated by a dielectric material or, in embodiments wherein the drive and sense lines are formed on the same side of a substrate, where the drive and sense lines are adjacent or nearly adjacent to each other. Touch sensors can also be arranged in any number of dimensions and orientations, including diagonal, concentric circle, and three-dimensional and random orientations. In order to scan a touch sensor panel and compute an image of touch, one or more frequencies can be used to stimulate one or more drive lines of the touch sensor panel (with the other drive lines being held at a fixed potential), and charge amplifiers (a.k.a. sense amplifiers) coupled to the sense lines can be configured to detect the amount of charge being coupled onto the sense lines. The outputs of the sense amplifiers, representing pixel output values, can be used in calculations to determine an image of touch for the touch sensor panel. Touch sensor panels capable of detecting either single-touch events or multiple touch events and determining an image of touch are described in Applicant's co-pending U.S. application Ser. No. 11/649,998 entitled “Proximity and Multi-Touch Sensor Detection and Demodulation,” filed on Jan. 3, 2007, the contents of which are incorporated by reference herein in their entirety for all purposes.
Before a touch sensor panel can be installed in a device, it is preferable to perform tests to at least ensure that there are no drive lines shorted together or open, and that no sense lines are shorted together or open. Conventional devices used to test touch sensor panels require a special fixture capable of supporting only the touch sensor panel and performing tests for shorts or opens on the drive and sense lines. To test for continuity (opens), conventional testing methods probe both ends of each line. Thus, for a touch sensor panel having N drive lines and M sense lines, a total of N×M tests must be performed just to test continuity. To test for shorts, each drive line is tested against every other drive line, and each sense line is tested against every other sense line. For P total lines, this can require P*(P−1)/2 tests. Alternatively or additionally, when the touch sensor panel is coupled to a subsystem circuit board via a flex circuit, a so-called “bed of nails” text fixture can be used to perform electrical tests on the subsystem circuit board, and while doing so, indirectly test for shorts between drive lines and shorts between sense lines on the touch sensor panel. In either case, because of the number of tests that are required, these types of tests can be very time consuming.